summaryrefslogtreecommitdiff
path: root/docs/tmpl/pangocairo.sgml
blob: da1d7e3f32950687b78eecad7d0bbbc0600cc1f6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
<!-- ##### SECTION Title ##### -->
Cairo Rendering

<!-- ##### SECTION Short_Description ##### -->
Rendering with the Cairo backend

<!-- ##### SECTION Long_Description ##### -->
<para>
The <ulink url="http://cairographics.org">Cairo library</ulink> is a
vector graphics library with a powerful rendering model. It has such
features as anti-aliased primitives, alpha-compositing, and
gradients. Multiple backends for Cairo are available, to allow
rendering to images, to PDF files, and to the screen on X and on other
windowing systems. The functions in this section allow using Pango
to render to Cairo surfaces.
</para>
<para>
Using Pango with Cairo is straightforward. A #PangoContext created
with pango_cairo_font_map_create_context() can be used on any
Cairo context (cairo_t), but needs to be updated to match the
current transformation matrix and target surface of the Cairo context
using pango_cairo_update_context(). The convenience functions
pango_cairo_create_layout() and pango_cairo_update_layout() handle
the common case where the program doesn't need to manipulate the
properties of the #PangoContext.
</para>
<para>
When you get the metrics of a layout or of a piece of a layout using
functions such as pango_layout_get_extents(), the reported metrics
are in user-space coordinates. If a piece of text is 10 units long,
and you call cairo_scale (cr, 2.0), it still is more-or-less 10
units long. However, the results will be affected by hinting
(that is, the process of adjusting the text to look good on the
pixel grid), so you shouldn't assume they are completely independent
of the current transformation matrix. Note that the basic metrics
functions in Pango report results in integer Pango units. To get
to the floating point units used in Cairo divide by %PANGO_SCALE.
</para>
<example id="rotated-example">
<title>Using Pango with Cairo</title>
<programlisting>
#include &lt;math.h>
#include &lt;pango/pangocairo.h>

static void
draw_text (cairo_t *cr)
{
#define RADIUS 150
#define N_WORDS 10
#define FONT "Sans Bold 27"

  PangoLayout *layout;
  PangoFontDescription *desc;
  int i;

  /* Center coordinates on the middle of the region we are drawing
   */
  cairo_translate (cr, RADIUS, RADIUS);

  /* Create a PangoLayout, set the font and text */
  layout = pango_cairo_create_layout (cr);
  
  pango_layout_set_text (layout, "Text", -1);
  desc = pango_font_description_from_string (FONT);
  pango_layout_set_font_description (layout, desc);
  pango_font_description_free (desc);

  /* Draw the layout N_WORDS times in a circle */
  for (i = 0; i &lt; N_WORDS; i++)
    {
      int width, height;
      double angle = (360. * i) / N_WORDS;
      double red;

      cairo_save (cr);

      /* Gradient from red at angle == 60 to blue at angle == 300 */
      red   = (1 + cos ((angle - 60) * G_PI / 180.)) / 2;
      cairo_set_rgb_color (cr, red, 0, 1.0 - red);

      cairo_rotate (cr, angle * G_PI / 180.);
    
      /* Inform Pango to re-layout the text with the new transformation */
      pango_cairo_update_layout (cr, layout);
    
      pango_layout_get_size (layout, &amp;width, &amp;height);
      cairo_move_to (cr, - ((double)width / PANGO_SCALE) / 2, - RADIUS);
      pango_cairo_show_layout (cr, layout);

      cairo_restore (cr);
    }

  /* free the layout object */
  g_object_unref (layout);
}

int main (int argc, char **argv)
{
  cairo_t *cr;
  FILE *f;

  if (argc != 2)
    {
      g_printerr ("Usage: cairo-example OUTPUT_FILENAME\n");
      return 1;
    }

  f = fopen (argv[1], "w");
  if (!f)
    {
      g_printerr ("Usage: cannot open '%s'\n", argv[1]);
      return 1;
    }

  cr = cairo_create();
  cairo_set_target_png (cr, f,
			 CAIRO_FORMAT_ARGB32,
			 2 * RADIUS, 2 * RADIUS);

  cairo_set_rgb_color (cr, 1.0, 1.0, 1.0);
  cairo_rectangle (cr, 0, 0, 2 * RADIUS, 2 * RADIUS);
  cairo_fill (cr);
  draw_text (cr);
  
  cairo_destroy (cr);
  fclose (f);

  return 0;
}
</programlisting>
</example>
<figure>
  <title>Output of <xref linkend="rotated-example"/></title>
  <graphic fileref="rotated-text.png" format="PNG"/>
</figure>

<!-- ##### SECTION See_Also ##### -->
<para>

</para>

<!-- ##### SECTION Stability_Level ##### -->


<!-- ##### STRUCT PangoCairoFontMap ##### -->
<para>

</para>


<!-- ##### FUNCTION pango_cairo_font_map_new ##### -->
<para>

</para>

@Returns: 


<!-- ##### FUNCTION pango_cairo_font_map_get_default ##### -->
<para>

</para>

@Returns: 


<!-- ##### FUNCTION pango_cairo_font_map_set_resolution ##### -->
<para>

</para>

@fontmap: 
@dpi: 
<!-- # Unused Parameters # -->
@dpi_x: 
@dpi_y: 


<!-- ##### FUNCTION pango_cairo_font_map_get_resolution ##### -->
<para>

</para>

@fontmap: 
@Returns: 


<!-- ##### FUNCTION pango_cairo_font_map_create_context ##### -->
<para>

</para>

@fontmap: 
@Returns: 


<!-- ##### FUNCTION pango_cairo_context_set_resolution ##### -->
<para>

</para>

@context: 
@dpi: 


<!-- ##### FUNCTION pango_cairo_context_get_resolution ##### -->
<para>

</para>

@context: 
@Returns: 


<!-- ##### FUNCTION pango_cairo_context_set_font_options ##### -->
<para>

</para>

@context: 
@options: 


<!-- ##### FUNCTION pango_cairo_context_get_font_options ##### -->
<para>

</para>

@context: 
@Returns: 


<!-- ##### FUNCTION pango_cairo_update_context ##### -->
<para>

</para>

@cr: 
@context: 


<!-- ##### FUNCTION pango_cairo_create_layout ##### -->
<para>

</para>

@cr: 
@Returns: 


<!-- ##### FUNCTION pango_cairo_update_layout ##### -->
<para>

</para>

@cr: 
@layout: 


<!-- ##### FUNCTION pango_cairo_show_glyph_string ##### -->
<para>

</para>

@cr: 
@font: 
@glyphs: 


<!-- ##### FUNCTION pango_cairo_show_layout_line ##### -->
<para>

</para>

@cr: 
@line: 


<!-- ##### FUNCTION pango_cairo_show_layout ##### -->
<para>

</para>

@cr: 
@layout: 


<!-- ##### FUNCTION pango_cairo_glyph_string_path ##### -->
<para>

</para>

@cr: 
@font: 
@glyphs: 


<!-- ##### FUNCTION pango_cairo_layout_line_path ##### -->
<para>

</para>

@cr: 
@line: 


<!-- ##### FUNCTION pango_cairo_layout_path ##### -->
<para>

</para>

@cr: 
@layout: